Posted
by
timothyon Wednesday June 22, 2005 @06:02AM
from the not-with-my-quanta-you-don't dept.

prostoalex writes "Vancouver, BC-based D-Wave Systems got $17.5 mln from Draper Fisher Jurvetson to work on a preliminary version of a quantum computer, Technology Review reports. Delivery date? Within three years: 'It won't be a fully functional quantum computer of the sort long envisioned; but D-Wave is on track to produce a special-purpose, "noisy" piece of quantum hardware that could solve many of the physical-simulation problems that stump today's computers, says David Meyer, a mathematician working on quantum algorithms at the University of California, San Diego.'"

Yah that was pretty much my thought too, who cares if the damn thing can calculate how to avoid an asteroid careening towards earth, the important factor to measure is compatability with first person shooters. I mean the physics thing isn't bad, it's just secondary to the truely important feature of all computers.

ignoring my typ-o of hertz
from the wikipedia article"A yottahertz (YHz) is a unit of frequency equal to a septillion hertz or a thousand zettahertz. "http://en.wikipedia.org/wiki/Yottahertz [wikipedia.org] 10^24

Well...I don't think trotting out Einstein's example everytime a theorist makes a surprising claim is very productive. What the parent post was pointing out is that there isn't an absolute correspondence between our mathematical formalisms of physical laws and physical reality itself. Surprising things happen when our experimental limits are pushed...the mathematical model holds or sometimes it breaks. Afterall, Einstein wasn't a science celebrity after the publication of his first papers. It took the s

The whole mania behind this technology is that somehow we will be able to pull correct data out of thin air using the magical properties of quantum units. Somehow eigenvalues will just instantaneously pop into existence by the careful selection of input parameters.

Too bad that's not how it works. These computers will still have to process data the same as any other processor and all the threat behind magically decoding 128-bit encryption is pure fluff. We are talking about another way of computing, for sure, but it is just another step in the evolution of computing systems rather than a brand new magic bullet for encryption maniacs.

It is also unclear why people want to build a "quantum computer" when it seems that simply putting it on a peripheral board and using it as a separate calculation machine seems to be a much more straightforward application of the device than trying to cram a whole computer with these chips.

when it seems that simply putting it on a peripheral board and using it as a separate calculation machine seems to be a much more straightforward application of the device than trying to cram a whole computer with these chips.

Yeah... quantum was a buzzword in 1905. But now it's actual science and proven. Quantum mechanics and QFT are two of the most successful theories to date. Yes there are conflicts with GR. And yes QM and QFT are most likely incomplete. However for a quantum computer there is no need for a theory that will supersede QM/QFT. The domain for quantum computing is well within the reach of QM itself.

Actually things like superdense coding and quantum teleportation have been verfied in the lab. So this stuff isn't exactly nonsense.

I agree with your statement except for the "But now it's actual science and proven."We have got to remember that no matter how much we like to think that science can prove something it can't the heart of the scientific theory is to disprove things in other words to be scientific a claim must be falsifiable [wikipedia.org]. Good theories remain just that, theories. Bad theories get falsified and thrown away. The quantum theories are good and so have endured thus far.

Falsification for a criterion of a valid theory is shaky at best. What is falsifiable? Surely we can all imagine possible worlds where all laws of physics are false. However can we make sense of world where these laws are false? What if time didn't flow at all? What if entropy decreased? Actually all theories are falsifiable and if there is a theory that isn't we shouldn't ignore it.

When I said "it's actual science and proven" I wasn't talking about if it's falsifiable or not. Also a falsifiable theory doe

IMHO, this business of "falsifiability" is used because falsifiable is a subset of testable. I think there may be theories which are testable but not falsifiable, but are isolated and pathological. When it actually comes down to doing science, however, I think many scientists take a utilitarian approach: how useful is Such-And-Such Theory for computing this or that quantity?

I suspect that the problem here is your use of the word proven, where I would have been happier with the word "demonstrated". Certainly the QM phenomena that we're talking about have been demonstrated, and that's a sufficient condition for us to take QC seriously.

With regards falsification, I'm not sure I agree that "Actually all theories are falsifiable". Theories that involve messing with reality can easily be made unfalsifiable, such as "we're all in a big computer game", a la The Matrix. There would

Yeah the area of QM that quantum computation deals with has no relevenace to GR. However one can not deny QM/QFT as a whole conflicts with GR in some areas. GR for example says mass curves spacetime however the spacetimes we deal with in QM/QFT are flat!

You can put a QFT on a curved space-time (but I don't know anything about this, suffice to say it's bloody hard and you get things like the Unrah effect and other acceleration anomalies). I think the problem is that quantum field theories of symmetric tensor fields (i.e., gravity) are non-renormalisable.

No you're right in QFT curved spacetimes appear but they make no sense. Hell the path integral method for minkowski space doesn't make sense either. Hence the Wick rotation. The problem that QFT on curved spactimes is paradoxical leads me to the conclusion that GR and QFT share properties that are incompatible.

It is, indeed, somewhat spooky that quantum bits can influence each other instantaneously over arbitrarily long distances (in case of entaglement), but for this "influence" to be used for any kind of useful infrormation transfer, transmission of classical information is required, thus limiting the effective transfer speed at light

As a layman, I don't understand this. If I fly to another star system with a code book and a quantum radio set, can't you send me information over it instantaneously?

Damn, I can't wait until we get gravity to work, so I can get my computer down on the desk.

Don't confuse engineering with science, the latter being largely concerned with measurable predictions and falsifiability. GR is also a remarkably good theory, and has been tested (according to some claims) to as many decimal places as QED.

(1) They never said the results are deterministic. As long as the result is okay 90% of the time, you can just repeat the measurement some number of times. As this gets large, the certainty in your answer can be made arbitrarily large. Just like in current digital computers: maybe a cosmic ray flips a bit, maybe a magnetic field causes a current to curve and arrive late. But the engineers have ensured that these problems occur below some tolerable rate.(one might worry that one has to repeat it so many

Good points. There are few "good" uses for quantum computers --- mainly, breaking public keys by factorising the product of two large primes (which may prove unrealisable in practise: I don't know how long one could keep an O(100) qbit state coherent), QM simulations (i.e., designable software experiments), and searching databases more quickly than classically possible. There will always be a need for classical computers.

I'm not sure I understand what you're getting at here. "Always" is a pretty long time (hence emphasis).

...as inventions go [classical computers] haven't even exhibited even an interesting longevity, much less irreplaceability.

Again, I'm probably missing your point, but what about healthcare, transport, communications, lifestyle, construction, entertainment, etc., etc.? One thing classical computers are good at is automation. How would

Again, I'm probably missing your point, but what about healthcare, transport, communications, lifestyle, construction, entertainment, etc., etc.? One thing classical computers are good at is automation. How would a quantum computer improve on a classical one in this respect?

The simple honest answer is that no one really knows, because quantum computing algorithm development is still in its infancy. That we have so many profound developments already (namely the enormous impact that the quantum simulation

With a (good enough) quantum computer it is possible to factor large numbers (Shor's algorithm) and to break various public key cryptography. (RSA, Elliptic curve crypto). So I would say that it is clear why people want to build one.

(Though it is expected to take a while before the quantum computers are good enough. A few years ago they built one that was able to factor the number 15...)

Yes, the pressing desire to read the mail of those people who haven't switched algorithms. Obviously this is worth spending billions on.

Or how about being able to solve the hardest math problems we have ever been able to think up as a species in mere seconds?

Shor's algorithm is great because we have been working on trying to understand the primes since the dawn of mathematics. You also dont seem to understand that once this takes hold, there will be no more public key algorithms. PKE is based on th

PKE is based on the idea that some math problems are harder to solve than to verify. Given a large enough quantum computer, that really is no longer the case.

The statement "quantum computers can break any public-key encryption" is probably not true.

For example, there are PK encryption schemes based on lattice problems (e.g., Ajtai-Dwork). No quantum algorithms are known for these lattice problems, despite lots of effort. Therefore, PKE may still be a viable approach even in the presence of quantum comp

That is possible, but I think that it will take some time after the invention of a large quantum computer before anybody puts much faith in assymetric crypto.

Sure, nobody may have an algorigthm to crack your digital signatures now, but there is considerable risk that one could emerge without warning, and anything you've transmitted in the past could have been saved and then cracked.

Some secrets only need to remain secret for a few days/weeks/months - nobody will worry about those. Some secrets need to re

Sure, nobody may have an algorigthm to crack your digital signatures now, but there is considerable risk that one could emerge without warning, and anything you've transmitted in the past could have been saved and then cracked.

This is true of public-key encryption, today, even with quantum computers out of the picture. An efficient factoring algorithm may be one clever insight away from reality.

Hell, someone could prove that P=NP "without warning," and then public-key crypto will really be impossible.

Together with quantum computers comes quantum criptography. Infact, the second one already exists in a very realibly form, although it is not commercially viable. It uses an initial data transfer to create a kind of public key. it is made on-the-fly and activelly by both sides, but it is still a kind public key.

QC is more of a key-exchange technology than a form of encryption. However it has a huge limitation - a physical link between whowever is attempting to communicate. Right now that means a fiber o

Well, first off, dwave already has solid state quantum computers, they are just freaking expensive, and for the number of qubits, it just isnt worth it at the moment.

Second, we all know that we are pretty far away from shors factorization algorithm, but at least with the technology that dwave is using (cooper pairs in superconductors), there is a chance of hitting that point sometime in the future.

NMR computers are fun to play with, and are pretty cheap for the number of qubits you can use, but will n

When quantum computing first hit the more "mainstream" press a few years ago it was hoped that they would start to be produced initailly close to the 10GHz mark. Anyone else got a more accurate figure these days?

GHz has no meaning with Quantum computers. Sorry.Clock speeds still do mean something in quantum computers. Arguably they're even more important than in classical computers, since in quantum computers you need to get operations done at least 10^4 times faster than the system's decoherence [wikipedia.org] time for quantum error correction to be robust. Decoherence times can be as short as microseconds, meaning that multiGHz operations could be important. Of course, if you're building a quantum computer, you want to work with a system with as long a decoherence time as possible....

... but it's not a proper quantum computer. It's based on tunneling, not entanglement. The latter is what everyone understands by the term 'quantum computer'. Their computer just requires knowledge of quantum theory to build it. Well, so do conventional computers...

but it's not a proper quantum computer. It's based on tunneling, not entanglement.

Nope, it is a quantum computer qubit. E.g. Google for "Cooper pair boxes"

This is a solid state quantum computer, an artifical atom, where the state could be encoded as the presence or absence of charge on an island. It tunnels on and off quantum mechanically, creating a qubit. Its just how the underlying system works.

Entanglement requires the coupling of more than one qubit, and is more part of the maths of QM. However, this may be done practically through capacitve or inductive coupling for the above devices.

It sounds like what they're describing is actually a set of Josephson junctions. People think those might be able to be used a viable qubits; however, the trick is having and maintaining coherence. This is what allows quantum computation. From the description they give of this system, it sound like they're not concerned with long term coherence, only with using tunneling to perform a sort of "annealing" algorithm to find the lowest energy state. So I think the grandparent it right, this is not a quantum computer in the ordinary sense.

Their qubits actually *are* entangled, as the various magnetic fields interact --- that's the whole point.

Not necessarily. It really all depends on how the decoherence time scale for this system relates to the strength of the interactions. It would still find the global minimum even if decoherence was very fast, because each dipole individually will still tunnel to a lower energy state.

This paper conjectures a new device called a Quantum Chaos Amplifier that magically pull an expremely small signal out of a superpositon. There is also a bit about it not being unitary which is a requirment for quantum circuits. I'm not sure this paper is anything but speculation.

People have been building quantum computers for years now. The biggest ones these days (around 14-qubits) are NMR quantum computers [qubit.org], although that technique appears to have scalability issues.

Seems to me that this is only news since they plan on selling quantum-CPU time.

This is somewhat offtopic, but I ran across it a few months ago and it's really interesting. QCL [tuwien.ac.at] allows you to write and run quantum algorithms. Runs on Linux and OS X with some tweaking.
The documentation that comes with it is really interesting, and gives some good insights into how quantum computing works and how to write programs for a quantum computer.

I realize modern tech support doesn't need to know much to anything about electronics or computer hardware's innerworkings... but I wonder if quantum computers will change that... and how many years of school will quantum tech support need?

===

It doesn't seem likely, but it'd be neat to have the title "Quantum Mechanic" EHEH!

In other news, CompTIA have released a working draft for their new Q+ exam - it's suitable for any engineer with 6 months' hands-on experience of Quantum Mechanics and GR. The pass mark is 80% and all 20 questions on the exam must be answered simultaneously.

"I realize modern tech support doesn't need to know much to anything about electronics or computer hardware's innerworkings."

That really depends on what you are supporting. Yea if you work for Dell you don't need to know an interrupt from a hole in the ground but if you working for NVidia supplying developer support yea you do.

One of the most interesting categories contains problems that are called NP-complete. These all have the feature that in order to solve the problem all possible solutions must be tried, and the number of possible solutions grows exponentially with the problem size.

"All possible solutions must be tried" is just wrong, and has nothing to do with NP-completeness.

I am not a Quantum Computing expert, but as far as I know there hasn't been much progress

It will, however, be ideally suited to solving problems like the infamous traveling-salesman problem . . . D-Wave's chip performs exactly this type of calculation automatically, in seconds.

How many seconds? Are they claiming that the travelling salesmen problem can be solved in polynomial time? This would be the biggest news to come out of the computer industry since the invention of the transistor. As far as I know, no quantum algorithms exist for solving NP complete problems such as the travelling salesmen problem. Can anyone here enlighten me?

We'll, it's kinda cheating. The algorithm is STILL NP, but in quantum computing we can run all paths in parallel so we solve all possible combinaisons at once, which becomes polynomial. However, we have no way of finding the good answer at 100%.

See, the problem in quantum computing is that you can have multiple states in parallel, but you can only 'read' one and lose all other states. This is like having a book with 400 pages, but when you open it, it selects (with a certain probability) a specific page and the whole book becomes that page, you lose all other pages.

We need to make the system converge/interfere in a meaningful way to the correct solution, and in its own way, this is the challenge of QC. In the end, if our algorithm works, we will be able to get the answer to the travelling salesman problem with a probability (depending how good our convergence is). Just like our book above, we need to increase the chance of opening the book on the page with the correct solution. This is non-trivial.

The thing is, the 'weight' of that convergence/meaningful interference, in problems like the travelling salesman, is usually as high as the time it takes to run the normal algorithm in classical computing. We end up not having much gains, it's not that fast. So, yes, if they are that good, we can solve the travelling salesman dilema in seconds... with a certain, probably very low %. Probably even a meaningless %.

However, in problems like finding if a function is unanimous(f(x)=0 or f(x)=1 for all x) or balanced (f(x)=0 for exactly half of x and f(x)=1 for exactly the other half of x) could be done in quantum computer with no errors and very fast, while in classical computing you'd have to try each value of x. If you however allow a certain % of error, the classical way with a stochastic computer would work best (test only a certain pool of value).

I'd love to see a quantum computer! That'd be so cool. And it's the only way to implement my perfect chess program.

But even if they do get this thing to succeed, with all the technical issues solved, the business model won't work. They want to sell solutions, not hardware? So company X asks a question, but the answer is only worthwhile if competing company Y can't ask the same question. The resolution is simple, company X will patent the question! Imagine how innovation can be stiffled now -- an order of

I am yet to see a description of a quantum computer that isn't plagued by decoherence problems. Basically, if you perturb a quantum computer by a small amount, e, then the wave function will diverge away from the idea state by exp(ket) for some constant k. So basically quantum computers will very rapidly start producing garbage. There are countless papers describing error correction but all this does is replace exp(ket) by exp(k'et) where k' is a bit smaller than k. Tthat exponential will still rapidly swallow the correction and give you decoherence before you can actually run anything. Some papers claim to get k right down to zero. But whenever you look you find they always make some assumtion about the system (ie. about various off diagonal terms in the Hamiltonian, the bits that give rise to these exponentials) and relaxing those assumptions ever so slightly (as is inevitable in the real world) brings back the exponential decay into decoherence.

One or two bit at a time quantum computers - sure, we can build those. My hunch, however, is that to build an N bit quantum computer is exp(N) hard. I expect we will eventually have non-trivial quantum computers, but unfortunately the amount of effort to make them will be as much as the effort to build a classical machine that can simulate them. This isn't just nay-saying, unlike the claims that driving at over 30mph would kill humans, my claims are backed up by many physicists, in particular those that don't have a financial interest in quantum computers.

On the other hand, quantum computer science is very interesting as a branch of mathematics and Shor's algorithm for factoring, for example, is a thing of beauty. So I don't blame people bluffing in order to get grant money. And I suppose I don't really hold it against researchers trying to get money out of venture capitalists this way either. Just as long as that money isn't coming out of any funds I'm investing in...

having a damned powerful computer in no way makes it easier for someone to design a bomb, as me having XCode makes it easy for me to write a program, as I can't actually program.

Forget building bombs. Filesharing is destroying the economy and will soon be classified as cyberterrorism. Just imagine what would happen if the pirates got their hands on a quantum computer. They'd suddenly be able to bittorrent all movies simultaneously. Such powerful technology could destroy civilization as we know it.

ETA were a possibility. They do fit the description "unhappy spaniards" rather well.

Well, they were a possibility (and they certainly are unhappy Spaniards), but you'll recall that the then-president of Spain also made that statement, which immediately turned out to be wrong, and he lost his office because of how wrong he was. There's a little more to it than that (in terms of Spanish politics in general), but there's certainly no question that it was Jihadists trying to change Spain's policy about suppo

Not sure about the ethics of that but it would certainly help solve the travelling salesmen problems.

SalesBoss: Salesman, use your sales skills and this new computer to visit all our target customers throughout the US as efficiently as you can.SalesMan: Computer, provide me with the most efficient route to our customers in the USComputer: Citizens in the US have been eliminated, your travel milage is Zero. Please stay where you are.

the one is a dererministic computing device (call it "pentium" or similar...;-) which basically makes use of quantum effects to implement smaller/faster/better transistors. that's all what this one boils down to: make better transistors and build the very same computers we made so far (of course, while trying to improve things like speed, energy usage, size, costs...)

the other is a whole new kind of devices. these are devices where bits of information are not re